This invention relates to an improvement in the processing of starch by the addition of a water soluble anionic polymer to starch slurries containing swollen starch granules resulting from treatment with cationic reagents in order to improve the dewatering of the slurry and thereby increase production rate and yield.
When starch is derivatized with one or more cationic reagents some of the granules become swollen or gelatinized. The presence of these swollen starch granules in the treated starch product reduces dewatering and drying rates and requires increased energy for drying. Moreover, when the treated starch is washed in a continuous centrifugal device such as a Merco the swollen starch granules are removed along with the reaction by-products due to their reduced density with respect to the intact granules. In these cases, while the processing rates are improved by the removal of some of the swollen starch, their removal reduces product yield and also contributes to increased effluent load.
Several synthetic polymers have heretofore been proposed as dewatering aids in processing such treated starch products, however, none to date have showed significant improvement in yields and processing rates when employed on a commercial scale.
In my copending application Ser. No. 282,353 filed July 13, 1981, now U.S. Pat. No. 4,345,948, issued Aug. 24, 1982, I found that the addition of specific cationic polymers to such starch slurries significantly improved the dewatering thereof. While the use of these cationic polymers is generally found to improve the dewatering of any slurry containing swollen starch granules, it has specific utility providing significant improvement in starch slurries resulting from treatment which lead to the production of nonionic or anionic starch derivatives and does not produce as dramatic an improvement in slurries containing derivatives resulting from cationic treatments.
It is therefore an object of the present invention to provide a method for processing treated starch containing swollen starch granules derived from cationic derivatization in order to maintain high processing rates without reducing the yield or increasing the effluent level.